1. Field of the Invention
This invention relates to an apparatus for controlling an internal combustion engine by controlling controlled-parameters (ignition timing and the like) for each cylinder in accordance with the period of reference-position areas in a reference-position signal, and more particularly to an apparatus for controlling an internal combustion engine, the reliability of which is improved by correcting an error of the period of the reference-position areas in the reference-position signal.
2. Description of the Related
In general, an internal combustion engine of a type revolved by a plurality of cylinders through a crank shaft comprises a microcomputer for calculating controlled-parameters (the fuel injection timing, the power supply timing to the ignition coil and the ignition timing and the like) in accordance with a reference-position signal synchronized with the revolutions of the internal combustion engine and the state of running informed from a variety of sensors.
Usually, timing for controlling ignition coils and injectors is, in a steady operational state, controlled by means of a timer in accordance with a reference position denoted by a reference-position signal. Therefore, an angle detection section for generating the reference-position signal is disposed on the crank shaft or the cam shaft of the internal combustion engine in order that first and last transitions of the reference-position signal indicate a predetermined crank angle (the rotational angle of the crank shaft), that is, the reference position.
The first and last transitions of the reference-position signal correspond to the timing, at which power is supplied to the ignition coil, and the ignition timing of the same respectively, which are realized in a start state (at the cranking timing) in which the rotational period is unstable and the operation of an ECU (Electronic Control Unit) is unstable due to the voltage drop.
FIG. 7 is a block diagram of the functions of a conventional internal combustion engine. FIG. 8 is a perspective view of an example of the structure of the angle detection section shown in FIG. 7. FIG. 9 is a graph showing both reference-position signal and a coil current generated by the angle detection section.
Referring to FIG. 7, reference numeral 1 represents a known angle detection section for generating reference-position signal SGT in the form of a pulse, the angle detection section 1 comprising, for example, as shown in FIG. 8: a rotational plate 12 attached to a cam shaft 10 of the internal combustion engine and having slits 11; and a photo-coupler having light receiving devices 13 and 14 respectively facing the slits 11.
The reference-position signal SGT generated by the angle detection section in synchronization with the revolutions of the internal combustion engine rises at reference position B75.degree. (at a position earlier than the top dead center by 75.degree.) and falls at reference position B5.degree. (at a position earlier than the top dead center by 5.degree.) of each cylinder.
Referring to FIG. 9, reference numeral T70 represents a period of areas (positions at each of which the crank angle is 70.degree.) in each of which the level of the reference-position signal SGT is high. Reference numeral T110 represents a period of areas (110.degree.) in each of which the same is low, T180 represents a period of the reference positions, and T720 represents a period of areas corresponding to the cylinders, the period being equivalent to one period (which is 720.degree. because the crank shaft is rotated by two times) corresponding to each cylinder. The pulse of the reference-position signal SGT corresponds to the number of the cylinders such that the pulse correspond to #1, #3, #4 and #2 cylinders if the internal combustion engine has four cylinders.
Symbols Ton represent a period in which the timer controls the timing to correspond to the moment at which the supply of coil current I is commenced. Symbol .theta.a represents the crank angle corresponding to the ignition timing and Ta represents a time controlled by the timer and corresponding to the ignition timing. In this case, the reference position for the power supply start timing Ton is B5.degree. and the time Ta controlled by the timer and corresponding to the ignition timing is B75.degree..
Referring to FIG. 7, reference numeral 2 represents variable sensors for detecting operational state D of the internal combustion engine and comprising a sucked-air quantity sensor, a throttle sensor and a temperature sensor (collectively omitted from illustration). Therefore, the operational state D includes the sucked-air quantity (or the degree of opening of the throttle) indicating the engine load, the revolution speed of the engine and the temperature of the sucked air.
Reference numeral 30 represents the ECU comprising a microcomputer to generate controlled-parameters (the fuel injection timing, the power supply timing, and the ignition timing and the like) for each cylinder in accordance with the reference-position signal SGT and the operational state D. Reference numeral 4 represents a power transistor having a base to which a controlled-parameter signal is supplied from the ECU 3 so that the power transistor 4 is activated/deactivated. Reference numeral 5 represents an ignition coil having a primary coil 5a connected to the collector of the power transistor 4. Reference numeral 6 represents a spark plug connected to a secondary coil 5b of the ignition coil 5 to sequentially burn mixed gas in each cylinder.
The ECU 30 comprises: a period measuring section 310 for measuring reference-position period T180 in accordance with the reference-position signal SGT; a timer control section 320 for calculating a controlled-parameter, for example, crank angle .theta.a at the ignition timing, in accordance with the reference-position signal SGT, the reference-position period T180 and the operational state D; a controlled-time setting section 330 for converting the ignition timing crank angle .theta.a into the time Ta controlled by the timer and corresponding to the ignition timing in accordance with the reference-position period T180; and an output interface 390 for supplying the time Ta controlled by the timer and corresponding to the ignition timing to the base of the power transistor 4, the time Ta controlled by the timer and corresponding to the ignition timing being supplied as the controlled-parameter signal.
The ECU 30 activates the power transistor 4 at the power supply start timing Ton (see FIG. 9) to raise the coil current I which flows through the primary coil 5a of the ignition coil 5. At the time Ta controlled by the timer and corresponding to the ignition timing, the ECU 30 deactivates the power transistor 4 to interrupt flowing of the coil current I. At the aforesaid timing, the ECU 30 makes the secondary coil 5b generate high-potential voltage so that the spark plug 6 discharges a spark.
Although FIG. 7 shows only the time Ta controlled by the timer and corresponding to the ignition timing for the ignition coil 5 as the controlled-parameter, the ECU 30 further generates a controlled-parameter for the injector (omitted from illustration) which corresponds to the fuel injection timing.
The angle detection section 1 may comprise a cylinder identification signal (omitted from illustration) for identifying a specific cylinder among the cylinders.
Referring to FIGS. 8 and 9, the operation of the conventional apparatus for controlling an internal combustion engine shown in FIG. 7 will now be described.
During running of the vehicle, the light receiving device 14 in the angle detection section 1 generates and supplies the reference-position signal SGT formed as shown in FIG. 9 in accordance with the revolutions of the cam shaft 10 of the internal combustion engine to supply the reference-position signal SGT to the ECU 30. Similarly, the various sensors 2 detect the operational state D indicating the number of revolutions and the load and the like and supply the operational state D to the ECU 30.
The period measuring section 310 in the ECU 30 measures the reference-position period T180 whenever it detects the reference position B75.degree. of the reference-position signal SGT.
The timer control section 320 calculates an optimum crank angle .theta.a at the ignition timing corresponding to the operational state D by using a provided map in accordance with the reference-position signal SGT and the reference-position period T180. In accordance with the reference-position period T180 and the crank angle .theta.a at the ignition timing, the controlled-time setting section 330 calculates the time Ta controlled by the timer and corresponding to the ignition timing (the time controlled by the timer counted from the reference position B75.degree.) corresponding to the ignition timing, as follows: EQU Ta=.theta.a x (T180/180.degree.) (1)
As described above, the timer control section 320, by using the map, calculates the optimum ignition timing .theta.a with reference to the reference position B75.degree.. The controlled-time setting section 330 calculates the time Ta controlled by the timer and corresponding to the ignition timing in accordance with Equation (1), the time Ta controlled by the timer and corresponding to the ignition timing being formed into the controlled-parameter signal through the output interface 390 and then supplied to the power transistor 4.
Although omitted from illustration in FIG. 7, assumption is made here that the power supply start timing Ton for the ignition coil 5 has been, as the timer controlled-time counted from the reference position B5.degree., transmitted through the output interface 390 and therefore the coil current I has been raised.
The time Ta controlled by the timer and corresponding to the ignition timing has been, as can be understood from Equation (1), normalized with the reference-position period T180 onto which the state of revolutions of the internal combustion engine are reflected. As a result, the coil current I can be interrupted at an optimum timing corresponding to the state of the revolutions so that the cylinders to be controlled can be ignited.
That is, the power transistor 4 is activated after the controlled time Ton has passed from the moment of the reference position B5.degree. so that the supply of the coil current I is commenced. After the time Ta controlled by the timer and corresponding to the ignition timing has passed from the reference position B75.degree., the power transistor 4 is deactivated and the coil current I is interrupted so that negative high-potential voltage is generated in the secondary coil 5b in accordance with the level of the coil current I realized at the interruption. Then, the high-potential voltage is applied to a space between electrodes of the spark plug 6 so that the spark plug 6 discharges a spark. As a result, the mixed gas in the cylinder, which is the subject to be controlled, is ignited.
However, the angle detection section 1 arranged as shown in FIG. 8 involves errors in the positions of the slits 11 due to scattering occurring when the same is manufactured, and accordingly the pulse edge of the reference-position signal SGT does not always accurately indicate the reference position B75.degree. or 5.degree..
If the first reference position B75.degree. is, in actual, at a crank angle position of 76.degree. shifted in the advance direction by 1.degree., the actual ignition timing is undesirably shifted in the advance direction by 1.degree. of the crank angle from an aimed ignition timing because the time Ta controlled by the timer and corresponding to the ignition timing obtainable from Equation (1) is determined on the basis of an assumption that the first reference position is B75.degree..
That is, the time Ta controlled by the timer and corresponding to the ignition timing does not coincide with a desired crank angle .theta.a at the ignition timing because the reference-position period T180 in Equation (1) equivalents to a crank angle of 181.degree..
It leads to a fact that the ignition is performed at an inaccurate timing shifted in the advance direction while being considerably deviated from the ignition timing calculated by the ECU 30. In this case, there arises a problem in that the internal combustion engine is damaged for example.
Since the conventional apparatus for controlling the internal combustion engine calculates the reference-position period T180 on a basis of an assumption that the reference-position signal SGT indicates the accurate reference positions B75.degree. and B5.degree. and calculates the controlled-parameters (for example, the time Ta controlled by the timer and corresponding to the ignition timing), accurate control cannot be performed if an error takes place in the reference position B75.degree. or B.degree. due to a manufacturing error or the like. For example, a problem rises in that the time Ta controlled by the timer and corresponding to the ignition timing is erroneously controlled, resulting in that the internal combustion engine is damaged.
FIG. 10 is a block diagram of the functions of another conventional apparatus for controlling an internal combustion engine of the foregoing type. FIG. 11 is a graph showing waveforms of a reference-position signal generated by the angle detection section 1 shown in FIG. 10 and a coil current.
Referring to FIG. 10, the structure in the ECU 3 is different from the control apparatus shown in FIG. 7. The residual portions are basically the same as those of the control apparatus shown in FIG. 7.
A reference-position signal SGT generated by the angle detection section 1 in synchronization with the revolutions of the internal combustion engine, as shown in FIG. 11, rises at a first reference position B75.degree. (at a position earlier than the top dead center by 75.degree.) and falls at a second reference position B5.degree. (at a position earlier than the top dead center by 5.degree.) for each cylinder. The reference-position period is 180.degree. of the crank angle.
Referring to FIG. 11, T180 (n-1) represents a previous reference-position period of the first reference positions B75.degree., T180 (n) represents a present reference-position period, Tex represents a predicated next period, Ton represents a time controlled by a timer corresponding to the timing at which supply of coil current I is commenced, .theta.a represents a crank angle corresponding to the ignition timing and Ta represents a time controlled by the timer and corresponding to the ignition timing. In this case, the reference position for the power-supply commencement timing Ton is the second reference position B5.degree. and the reference position for the time Ta controlled by the timer and corresponding to the ignition timing is the first reference position B75.degree..
Reference numeral 3 represents an ECU comprising a microcomputer to generate controlled-parameters (the fuel injection timing, the power supply timing, and the ignition timing and the like) for each cylinder in accordance with the reference-position signal SGT and the operational state D.
The ECU 3 comprises: a period measuring section 31 for measuring reference-position period T180 in accordance with the reference-position signal SGT; a controlled-parameter calculating section 320 for controlling the controlled-parameters in accordance with the reference-position signal SGT, the reference-position period T180 and the operational state D; and an output interface 39 for supplying the controlled-parameter to the base of the power transistor 4 as a drive signal.
The controlled-parameter calculating section 32 comprises: a predicted-period calculating section 33 for calculating the next reference-position period, that is, the predicted period Tex, in accordance with change in the reference-position period T180; a timer control section 34 for, by using a map, calculating the power-supply commencement timing Ton and the crank angle .theta.a at the ignition timing to serve as the controlled-parameters in accordance with the reference-position signal SGT, reference-position period T180 and the operational state; and a correction section 35 for calculating to correct the crank angle .theta.a at the ignition timing in accordance with the predicted period Tex so as to transmit the ignition timing Ta.
The controlled-parameter signal supplied from the ECU 3 activates the power transistor 4 at the power-supply timing Ton so that the coil current I, which flows through the primary coil 5a of the ignition coil 5, is raised. The controlled-parameter signal deactivates the power transistor 4 at the time Ta controlled by the timer and corresponding to the ignition timing to interrupt the coil current I so that high-potential voltage is generated in the secondary coil 5b to cause the spark plug 6 to discharge a spark.
Although only the controlled-parameter for the ignition coil 5 has been described here, the ECU 3 further generates, for example, a controlled-parameter for the injector (omitted from illustration) corresponding to the fuel injection timing similarly to the apparatus shown in FIG. 7.
Referring to FIGS. 8 and 11, the operation of the conventional apparatus for controlling an internal combustion engine shown in FIG. 10 will now be described.
During running of the vehicle, the light receiving device 14 in the angle detection section 1 generates and supplies the reference-position signal SGT formed as shown in FIG. 11 in accordance with the revolutions of the cam shaft 10 of the internal combustion engine to supply it to the ECU 3. Similarly, the various sensors 2 detect the operational state D indicating the number of revolutions and the load and the like and supplies the operational state D to the ECU 3.
The reference-position period measuring section 31 in the ECU 3 measures the period as the reference-position period T180 whenever it detects the first reference position B75.degree..
The predicted-period calculating section 33 in the controlled-parameter calculating section 32 calculates the predicted period Tex in accordance with the previous reference-position period T180 (n-1) and the present position period T180 (n) as follows: EQU Tex=T180 (n)+K{T180 (n)-T180 (n-1)} (2)
where {T180 (n)-T180 (n-1)} represents a deviation of the period corresponding to change in the revolutions and K represents a prediction weighted coefficient. The prediction weighted coefficient K is set to an optimally matched value corresponding to acceleration characteristics and the like of each internal combustion engine.
AS shown in Equation (2), a value obtained by multiplying the deviation of the period with the prediction weighted coefficient K is added to the present position period T180 (n) to be reflected on the predicted period Tex.
Since the deviation of the period is, therefore, a negative value in, for example, the transition operational state during acceleration because T180 (n)&lt;T180 (n-1), the quantity of decrease in the reference-position period T180 is reflected on the predicted period Tex. In a steady operational state in which change in the revolutions is limited, the previous reference-position period T180 (n-1) and the present reference-position period T180 (n) are the same, and therefore, the deviation in the period is made to be substantially zero. Accordingly, the present reference-position period T180 (n) is made to be the predicted period Tex as it is.
Then, the timer control section 34 in the controlled-parameter calculating section 32 calculates optimum power-supply commencement timing Ton and the crank angle .theta.a at the ignition timing corresponding to the operational state D. The correction section 35 calculates to correct the time Ta controlled by the timer and corresponding to the ignition timing (the controlled time from the first reference position B75.degree.) corresponding to the ignition timing in accordance with the crank angle .theta.a at the ignition timing and the predicted period Tex as follows: EQU Ta=.theta.a (Tex/180.degree.) (3)
The crank angle .theta.a at the ignition timing in Equation (3) corresponds to the ignition timing from the controlled reference position (B75.degree.).
As described above, the controlled-parameter calculating section 32, by using a map, obtains the optimum ignition timing .theta.a corresponding to the operational state D with reference to the first reference position B75.degree. (or the second reference position B5.degree.) to calculate the timer control time to the ignition timing, that is, the ignition timing Ta from Equation (3). The ignition timing Ta is transmitted through the output interface 39.
The power supply start timing Ton for the ignition coil 5 has been, as the timer controlled time from the second reference position B5.degree., transmitted through the output interface 39, and therefore the coil current I has been raised. Therefore, the ignition timing Ta corrected with the predicted period Tex interrupts the coil current I at an optimum timing so that the cylinder, which is the subject to be controlled, can be ignited.
That is, when the supply of the coil current I is commenced after the control time Ton has passed from the second reference position B5.degree. and the power transistor 4 is deactivated after the control time Ta has passed from the first reference position B75.degree. so that the coil current I is interrupted, negative high-potential voltage is applied to the spark plug 6 connected to the secondary coil 5b of the ignition coil 5. Therefore, discharge takes place between the electrodes of the spark plug 6 of the cylinder, the ignition of which is the subject to be controlled, so that the mixed gas in the cylinder to be subjected is ignited.
However, the angle detection section 1 in the apparatus for controlling an internal combustion engine as well as involves errors in the positions of the slits 11 due to scattering occurring when the same is manufactured, and accordingly the pulse edge of the reference-position signal SGT does not always accurately indicate the reference position B75.degree. or 5.degree..
If the first reference position B75.degree. is, in actual, at crank angle position 76.degree. shifted in the advance direction by 1.degree., the actual ignition timing is undesirably shifted in the advance direction by 1.degree. of the crank angle from an aimed ignition timing because the time Ta controlled by the timer and corresponding to the ignition timing obtainable from Equation (3) is determined on the basis of an assumption that the first reference position is B75.degree..
It leads to a fact that the ignition is performed at an inaccurate timing shifted in the advance direction while being considerably deviated from the ignition timing calculated by the ECU 3. In this case, there arises a problem in that the internal combustion engine is damaged for example.
Since the conventional apparatus for controlling an internal combustion engine has been arranged in this way that the predicted period Tex is calculated and the controlled-parameter for the ignition coil 5 is obtained on the basis of an assumption that the reference-position signal SGT accurately indicates the reference positions B75.degree. and B5.degree., the apparatus cannot precisely control the internal combustion engine similarly to the foregoing control apparatus if the reference position B75.degree. or B5.degree. includes an error due to a manufacturing error or the like. Accordingly, there arises a problem in that the controlled-parameter, for example, the time Ta controlled by the timer and corresponding to the ignition timing is erroneously controlled and therefore the internal combustion engine can be damaged.